This morning's adventure turned out to be an unexpectedly thrilling walk along the Golden Orb Trail at Long Key State Park, along which we saw a bird that is super-rare in the US (a female Zenaida dove). Afterwards, we decided to drive toward the campgrounds at the western end of the park, where according to my BenchMap app, there was a tri-station that had never been recovered since its monumentation in 1972.
At first glance, it appeared we might be able to make an easy recovery. The area was relatively open, and right away we spotted some of the objects referred to in the description (the gate leading to the campground area, the chain-link fence, and the power pole with guy wire). But since it's a tri-station, we could expect the coordinates to take us directly to the station ... which was apparently beneath heavy sea grape cover. Even if we had been able to penetrate the sea grape, the monument—set flush with the surface in 1972—would be concealed beneath several inches of sea grape and other vegetation debris.
We had a similar experience when looking for both reference marks—they're probably still in place, but without a metal detector and plenty of time to search, they will stay hidden beneath the grass and other foliage.
The Australian pines that were used as references were nowhere to be found; perhaps they were torn up in a storm, or maybe—because they are invasive and allelopathic—they were removed at some point to allow native vegetation to flourish? All we saw near the site of the station were large stands of sea grape, and grasses near the sites of the reference marks.
It is likely that the marks still exist, but recovery would require moderate labor and perhaps a metal detector to pinpoint their locations.